Fundulus olivaceus (Storer, 1845)

Species Name and Body Length

The blackspotted topminnow, Fundulus olivaceus, has an elongated body that reaches up to 9.7 centimetres (3.8 in) in length.

Body Coloration and Markings

Its upper body is brownish yellow to olive green, marked by a wide dark lateral band and distinct dark spots.

Sexual Dimorphism and Breeding Fin Traits

Males have longer fins than females, and their fins may turn yellowish during the breeding season.

Similar Species Comparison

This species is very similar to the blackstripe topminnow (Fundulus notatus), which also has a dark lateral band, but can be distinguished by its darker, more numerous spots. The two species are known to hybridize.

Gill Slit Morphology

In F. olivaceus, the gill slit extends dorsally to the uppermost pectoral fin ray.

Dorsal Fin Position Measurement

The distance from the origin of the dorsal fin to the end of the hypural plate is less than the distance from the dorsal fin origin to the preopercle, or occasionally equal to this distance.

Mouth Position

The mouth is slightly supraterminal.

General Habitat

Blackspotted topminnows live near the surface of quiet or flowing, relatively clear headwaters, creeks, and small rivers with sand-gravel bottoms.

Microhabitat Associations

They are often found along margins near thick stands of emergent vegetation.

Gulf Slope Distribution

The distribution of the blackspotted topminnow covers the Gulf Slope from the Galveston Bay drainage in Texas, east to the Choctawhatchee River system in Florida, and the middle Chattahoochee River drainage in Georgia.

Mississippi River Basin Distribution

It also occupies the Mississippi River basin from the Gulf north to southeastern Kansas, central Missouri, southern Illinois, western Kentucky, and eastern Tennessee.

Spawning Season

The spawning season of the blackspotted topminnow runs from March to early September, with peak spawning in May.

Male Territoriality

Large males have occasionally been observed defending open territories of three square meters.

Wild Male-Female Interactions

In the wild, males rarely tolerate females except during spawning activity in the morning or evening.

Captive Aggression Traits

In aquariums, this fish loses its wild traits and becomes less aggressive, though males will redevelop their wild aggressive traits when spawning approaches.

Male-Male Agonistic Behavior

Males will approach each other head-on, flare their opercula and gular areas in a behavior very similar to cichlids or bettas, then slap and bite each other's flanks until one individual retreats.

Egg Size

Ripe eggs average 2.14 mm in diameter.

Egg Membrane Structure

The outer membrane of the egg has filaments that are typically concentrated in one area to form a tuft.

Hatching Time and Lifespan

The eggs hatch in 10–14 days, and the fish has a total lifespan of around 3 years.